FIG. 4 shows a cross section of a conventional gas laser apparatus, and FIG. 5 shows a cross section taken along the line H--H of FIG. 4. A case 51 shown in FIGS. 4 and 5 is closed with a cap 52. The case 51 and the cap 52 are each formed of an insulating material. A gas medium is enclosed in a chamber defined by the case 51 and the cap 52. A certain voltage is applied between a cathode 58 and an anode 59 to cause electric discharge therebetween and to thereby generate laser light. The generated laser light is emitted out of the case 51 through a window 60 formed in the case 51, as indicated by arrow K.
A blower 53 serves to circulate the gas medium in the case 51 as indicated by arrows D and E. A heat exchanger 61 constituted of a plurality of pipes serves to cool the gas heated by the discharge. The blower 53 has shafts 53a and 53b for its rotation. The shafts 53a and 53b are supported on bearings 56 and 57 which are in turn supported on bearing boxes 54 and 55. Grease or oil which does not easily evaporate is used as a lubricant for lubricating the bearings 56 and 57.
There is a problem to be solved in this conventional apparatus. That is, the lubricant such as grease or oil is not only evaporated but is also released from the bearings as small particles having a size of several microns to be diffused in the gas medium in the case 51. The lubricant diffused in the case 51 is decomposed by electric discharge into materials which are impurities in the gas medium, so that the life of the gas medium is shortened. In particular, in the case of an excimer laser apparatus using halogen gas having high reactivity, such impurities react with the halogen gas to produce halides which badly influence the performance of the apparatus in such a manner as to impede laser oscillation and to reduce the life of the gas medium.